Base‐Free Selective Deaminative Suzuki Coupling of Heterocyclic Azaindole and Picolinaldehyde‐Based Scaffolds: Promising Substitutes for NLO Materials

ABSTRACT Six novel azaindole‐ and picolinaldehyde‐based derivatives ( Aza‐1 to Aza‐3 and Nic‐1 to Nic‐3 ) were synthesized through the condensation of salicylaldehyde with corresponding thiosemicarbazones via a base‐free nickel‐catalyzed reflux‐assisted deaminative Suzuki coupling, affording excellent yields. Their electronic, optical, and nonlinear optical (NLO) characteristics were systematically explored using the M06/6‐311G(d,p) functional. The analysis encompassed natural bonding orbitals, frontier molecular orbitals, global reactivity parameters, density of states, UV–visible spectra, and transition density matrix studies. The minimum energy gaps (E_gap) of 4.703 eV for Aza‐1 and 4.414 eV for Nic‐3 indicated enhanced charge‐transfer behavior. Correspondingly, these molecules exhibited the lowest global hardness (2.351 and 2.207 eV) and highest softness (0.213 and 0.227 eV), confirming their higher chemical reactivity. Significant first‐order hyperpolarizabilities (β_total) were observed for Aza‐3 (6.89 × 10 −3 ⁰ esu) and Nic‐3 (2.67 × 10 −2 ⁹ esu), while Aza‐3, Nic‐2, and Nic‐3 displayed remarkable second‐order hyperpolarizabilities (γ_total = 8.69 × 10 −3 ⁵, 9.60 × 10 −3 ⁵, and 9.24 × 10 −3 ⁵ esu, respectively), far exceeding that of p‐nitroaniline (7.29 × 10 −3 ⁶ esu). Overall, the findings highlight the synthesized chromophores as promising candidates for high‐performance NLO and optoelectronic applications.